linux-kernel - Re: [PATCH v3] x86, pmem: fix broken __copy_user

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Message-ID: <20170411154913.GA20725@linux.intel.com>
Date:   Tue, 11 Apr 2017 09:49:13 -0600
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     linux-nvdimm@...ts.01.org, Jan Kara <jack@...e.cz>,
        Toshi Kani <toshi.kani@....com>,
        Matthew Wilcox <mawilcox@...rosoft.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Christoph Hellwig <hch@....de>, Jeff Moyer <jmoyer@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Re: [PATCH v3] x86, pmem: fix broken __copy_user_nocache
 cache-bypass assumptions

On Mon, Apr 10, 2017 at 05:35:02PM -0700, Dan Williams wrote:
> Before we rework the "pmem api" to stop abusing __copy_user_nocache()
> for memcpy_to_pmem() we need to fix cases where we may strand dirty data
> in the cpu cache. The problem occurs when copy_from_iter_pmem() is used
> for arbitrary data transfers from userspace. There is no guarantee that
> these transfers, performed by dax_iomap_actor(), will have aligned
> destinations or aligned transfer lengths. Backstop the usage
> __copy_user_nocache() with explicit cache management in these unaligned
> cases.
> 
> Yes, copy_from_iter_pmem() is now too big for an inline, but addressing
> that is saved for a later patch that moves the entirety of the "pmem
> api" into the pmem driver directly.
> 
> Fixes: 5de490daec8b ("pmem: add copy_from_iter_pmem() and clear_pmem()")
> Cc: <stable@...r.kernel.org>
> Cc: <x86@...nel.org>
> Cc: Jan Kara <jack@...e.cz>
> Cc: Jeff Moyer <jmoyer@...hat.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Christoph Hellwig <hch@....de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Matthew Wilcox <mawilcox@...rosoft.com>
> Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
> Signed-off-by: Toshi Kani <toshi.kani@....com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>

This looks good to me, thanks for fixing this.

Reviewed-by: Ross Zwisler <ross.zwisler@...ux.intel.com>